The invention relates to a directional coupler.
A directional coupler has been disclosed, for example, in DE 23 20 458 C2. This comprises an asymmetric stripline and a coaxial line, and the stripline in this directional coupler is coupled to the coaxial inner conductor. The strip conductor is in this case fitted in the coupling zone into an exposed cutout in the outer conductor of the coaxial line, with the ground conductor of the stripline at the same time forming the shield (which is interrupted by the cutout) of the coaxial line.
A directional coupler which is to this extent comparable to this prior art has also been disclosed in DE 199 28 943 A1. In order to provide inductive coupling as well in a directional coupler such as this, this prior publication proposes that the base plate be in the form of a circular substrate wafer which is seated in an appropriately cylindrical milled-out area. The angle of the substrate wafer can thus be rotated with the coupling piece.
The directional coupler can thus be tuned by rotating the coupling line in the electromagnetic coaxial cable field. However, the tuning is in this case restricted just to the coupling loss. The achievement of a high degree of directionality, as is of major importance in practice, plays no role in this solution.
The directional coupling signal variables which are tapped off in the cited prior art are supplied in a known manner to an external evaluation device, to be precise via coaxial cables. Since radio-frequency signals are emitted, high-quality and costly coaxial cables must therefore also be used, in the same way as high-quality and costly coaxial plug connectors as well, of course. The aim of this is to ensure that a high-quality connection and thus good directionality can also be achieved, with respect to the characteristic impedance.
Equally, only comparatively poor directionality levels can be achieved with the known directional couplers.
Against the background of the prior art in this field, the object of the present invention is thus to provide an improved directional coupler which allows better signal values to be achieved with the design whose cost is lower overall.